Other research has also overwhelmingly found a dose-response association between traumatic childhood experience and addiction. For example, the long-term Adverse Childhood Experiences study, conducted jointly by researchers from the Centers for Disease Control and Prevention and Kaiser Permanente found that the more trauma people experienced in childhood, the more likely they were to develop addiction later on.

The researchers examined the medical histories of some 17,000 people insured by Kaiser Permanente in California and interviewed them about their childhood histories. The authors were looking for evidence of 10 categories of potentially traumatic “adverse childhood experiences” (ACEs), including physical abuse, emotional abuse, sexual abuse or loss of a parent to death or divorce.

Then, by comparing people with no ACEs with those who had one or more ACEs, the researchers found a profound dose-dependent effect of trauma on addiction risk: a boy with four ACEs, for instance, is five times more likely to become an alcoholic than someone who has none; he is also 46 times more likely to become an intravenous drug user than a person with no ACEs.

“The general concept of addiction is that it is caused by properties intrinsic in certain chemicals. For example, you take heroin enough times and then you can’t stop using. What we found is the opposite,” says study leader Dr. Vincent Felitti, former chief of preventive medicine at Kaiser Permanente in San Diego. “The underlying dynamics of addiction are related to underlying life experience.”

Fortunately, most people are resilient to trauma. Two to three years after 9/11, data show that only 12% of recovery workers who worked on “the pile” after the attacks still had symptoms of PTSD. There are many protective factors that keep people from suffering from trauma long-term, but one such factor — which can be sought and provided by anyone — may also help those whose mental-health problems persist: social support.

“Social support is probably the single most clear driver that mitigates the consequences of trauma,” says Galea. “It’s central.”

Indeed, lack of social support is linked with addiction and poor mental health. “Social support is a huge factor,” says Felitti.

It has been undoubtedly difficult this week, with the 10th anniversary of 9/11 approaching, to avoid the media coverage and the reminders of the attacks. But to help put the trauma of the event behind you — and to help keep yourself and your loved ones resilient — one of the best things to do is be a good friend, parent, spouse, child or neighbor, and reach out to those whose social networks may be frayed.

Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.